Protective helmet with impact-absorbing layer

ABSTRACT

A protective helmet can reduce the likelihood of a player sustaining a brain injury while engaging in a contact sporting event. The helmet can include a hard outer shell with exterior and interior surfaces. The helmet can include an impact-absorbing layer adjacent to the interior surface of the outer shell. The impact-absorbing layer can have a base layer and flexible raised portions extending from the base layer toward the interior surface of the outer shell. During a collision with another player, the flexible raised portions can topple over to allow the outer shell to rotate relative to the impact-absorbing layer. The flexible raised portions can topple over and increase the duration of a collision, thereby reducing the peak rotational acceleration experienced by the player&#39;s head&#39;s center of gravity and, in turn, reducing the likelihood of the player sustaining a brain injury from the collision.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 61/938,628 filed Feb. 11, 2014, which is hereby incorporated by reference in its entirety as if fully set forth in this description.

FIELD

This disclosure relates to impact-absorbing layers, protective helmets with impact-absorbing layers, and methods of manufacturing impact-absorbing layers.

BACKGROUND

Research has shown that rotational acceleration, which is often encountered during contact sports, can result in traumatic brain injuries in participants. Specifically, when a participant's brain is subjected to rotational acceleration during a collision with another player, portions of the brain (e.g. portions having differing densities and distances from an axis of rotation) slide over one another, thereby stretching axons that traverse junctions between white and grey matter in the brain. This sliding action can result in tearing, shearing, or twisting of brain axons, resulting in traumatic brain injuries. Existing helmets are designed to protect a participant's brain from damage caused by linear acceleration but fail to adequately protect the participant's brain from damage caused by rotational acceleration. Accordingly, there is a strong need for a new helmet that protects a participant's brain from damage caused by linear acceleration and also rotational acceleration.

SUMMARY

This disclosure presents impact-absorbing layers, protective helmets with impact-absorbing layers, and methods of manufacturing impact-absorbing layers.

In one example, a protective helmet can include a hard outer shell having an exterior surface and an interior surface. The protective helmet can include an impact-absorbing layer adjacent to and conforming to the interior surface of the hard outer shell. The impact-absorbing layer can include a base layer and a plurality of flexible raised portions extending from the base layer. The plurality of flexible raised portions can each have a base portion wider than an end portion. The end portions of the flexible raised portions can extend to and contact the interior surface of the hard outer shell. The end portions of the plurality of raised portions can be affixed to or captured in pockets or indentions on the interior surface of the hard outer shell. The plurality of flexible raised portions can be made of microcellular urethane foam having a density of about 1-30 pounds per cubic foot. The microcellular urethane foam can be a mechanically frothed microcellular urethane foam. The urethane foam can have a density of about 10-20, 10-18, or 12-18 pounds per cubic foot. The plurality of flexible raised portions can each be defined by a side angle, a top radius, and a base radius. The side angle can be about 1-30, 10-20, or 15 degrees. The base radius can be about 0.005-1.5, 0.125-0.5, or 0.125-0.25 inches, and the top radius can be about 0.005-1.0, 0.125-0.5, or 0.125-0.25 inches.

The protective helmet can include an adjustable suspension system having a fabric layer configured to conform to a portion of a wearer's head and a plurality of tethers extending from the fabric layer to the outer shell to flexibly secure the fabric layer to the hard outer shell and capture the impact-absorbing layer between the fabric layer and the hard outer shell. The tethers can be configured to allow the hard outer shell to rotate relative to the fabric layer during an impact event as one or more of the plurality of flexible raised portions topple over.

An adjustable suspension system can include a first fabric layer configured to conform to a front portion of a wearer's head and a second fabric layer configured to conform to a rear portion of the wearer's head. The first fabric layer can attach to the second fabric layer at a first attachment point along a left side of the wearer's head and at a second attachment point along a right side of the wearer's head. The adjustable suspension system can include a tensioning strap extending from the first attachment point to the second attachment point and having a chin cup configured to be secured against a wearer's chin. The adjustable suspension system can include a plurality of tethers extending from the first and second fabric layers to the hard outer shell to flexibly secure the first and second fabric layers to the hard outer shell and to capture the impact-absorbing layer between at least one of the first and second fabric layers and the hard outer shell. The plurality of tethers can be configured to allow the hard outer shell to rotate relative to the first and second fabric layers during an impact event as one or more of the plurality of raised portions topple over.

The base layer of the impact-absorbing layer can include an indentation on a bottom surface of the base layer beneath one of the plurality of flexible raised portions. The indentation can be configured to provide a cavity in the impact-absorbing layer to increase an initial compression rate of the flexible raised portion during an impact event. The impact-absorbing layer can include a vent extending from a top surface of the impact-absorbing layer to the indentation on the bottom surface of the impact-absorbing layer. Compressing the flexible raised portion during an impact event can collapse the raised portion downward into the cavity formed by the indentation thereby forcing air out of the cavity through the vent. The air that is forced out of the cavity is capable of transporting heat and perspiration away from the player's head, thereby cooling the player's head and helping to prevent heat exhaustion.

In another example, a protective helmet can include a hard outer shell having an exterior surface and an interior surface. The protective helmet can include an adjustable suspension system having a fabric layer configured to fit snugly over a portion of a wearer's head. The fabric layer can be flexibly connected to the interior surface of the hard outer shell by two or more tethers. The fabric layer can be connected to a chin cup by a tensioning strap, and tightening the tensioning strap can simultaneously draw the chin cup against a wearer's chin and draw the fabric layer against the portion of the wearer's head. The protective helmet can include an impact-absorbing layer captured between the fabric layer and the hard outer shell. The impact-absorbing layer can include a plurality of flexible raised portions extending outward from a base layer toward the interior surface of the hard outer shell. End portions of the plurality of raised portions can be affixed to or captured by pockets or depressions on the interior surface of the hard outer shell. The hard outer shell can be configured to rotate relative to the fabric layer during an impact event as the flexible raised portions of the impact-absorbing layer topple over.

The impact-absorbing layer can be made of a microcellular urethane foam. The microcellular urethane foam can have a density of about 10-20, 10-18, or 12-18 pounds per cubic foot. The plurality of flexible raised portions each have a side angle, a top radius, and a base radius. The side angle can be about 1-30, 10-20, or 15 degrees. The base radius can be about 0.005-1.5, 0.125-0.5, or 0.125-0.25 inches. The top radius can be about 0.005-1.0, 0.125-0.5, or 0.125-0.25 inches.

The base layer can include an indentation on a bottom surface of the base layer beneath one of the plurality of raised portions. The indentation can be configured to provide a cavity in the impact-absorbing layer to increase an initial compression rate of the raised portion during an impact event. The impact-absorbing layer can include a vent extending from a top surface of the impact-absorbing layer to the indentation on the bottom surface of the impact-absorbing layer. Compressing the flexible raised portion during an impact event can collapse the raised portion downward into the cavity formed by the indentation thereby forcing air out of the cavity through the vent. The air forced out of the cavity is capable of transporting heat and perspiration away from the player's head, thereby cooling the player.

In yet another example, an impact-absorbing layer can include a base layer and one or more flexible raised portions extending from the base layer. Each of the one or more flexible raised portions can have a base portion wider than an end portion. The one or more flexible raised portions can each be defined by a side angle, a top radius, and a base radius, where the angle is about 10-20 degrees, where the base radius is about 0.05-1.0 inches, where the top radius is about 0.05-1.0 inches, where the base layer has a thickness of about 0.1-1.3 inches, and where the impact-absorbing layer is made of a microcellular urethane foam having a density of about 12-18 pounds per cubic foot. The microcellular urethane foam can be a mechanically frothed urethane foam formed by a manufacturing process that includes casting a liquid froth onto a substrate, heat curing the liquid froth to form a solid urethane foam, and coating the solid urethane foam with a continuous skin made of a thermoplastic elastomer. The substrate can be a mold having a shape that produces a solid urethane foam having a shape corresponding to an impact-absorbing layer with flexible raised portions extending from a base layer.

Additional objects and features of the invention are introduced below in the Detailed Description and shown in the drawings. While multiple embodiments are disclosed, still other embodiments will become apparent to those skilled in the art from the following Detailed Description, which shows and describes illustrative embodiments. As will be realized, the disclosed embodiments are susceptible to modifications in various aspects, all without departing from the scope of the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detailed Description below. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended that this Summary be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTIONS OF DRAWINGS

FIG. 1 shows a football helmet having a hard outer shell and an impact-absorbing layer proximate an interior surface of the hard outer shell.

FIG. 2 shows a cross-sectional view of a protective helmet with an impact-absorbing layer captured between an interior surface of a hard outer shell and an inner fabric layer where the inner fabric layer is connected to the hard outer shell by a plurality of tethers in a relaxed state.

FIG. 3 shows a cross-section view of the protective helmet of FIG. 2 during an impact event where a tangential force is imparted to an outer shell of the sports helmet causing rotation of the hard outer shell relative to the inner fabric layer, where a portion of the tangential force is dissipated as flexible raised portions of the impact-absorbing layer topple over during the impact event.

FIG. 4 shows a portion of an impact-absorbing layer having a raised portion extending from a base layer, the raised portion having a height, a side angle, a first density, a base radius, and a top radius, and the base layer having a thickness and a second density.

FIG. 5 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer, the base layer having a thickness that is about 30% of the height of the raised portions.

FIG. 6 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer, the base layer having a thickness that is about 30% of the height of the raised portions.

FIG. 7 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer, the base layer having a thickness that is about 30% of the height of the raised portions.

FIG. 8 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer, the base layer having a thickness that is about 10-15% of the height of the raised portions.

FIG. 9 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer, the base layer having a thickness that is about 30% of the height of the raised portions.

FIG. 10 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer, the raised portions having a relatively large base radius.

FIG. 11 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer, the base layer having a thickness that is about 200% of the height of the raised portions.

FIG. 12 shows an impact-absorbing layer having a plurality of raised portions extending from a first base layer, which is positioned on top of a second base layer formed from a higher or lower density material.

FIG. 13 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer.

FIG. 14 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer.

FIG. 15 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer.

FIG. 16 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer.

FIG. 17 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer.

FIG. 18 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer, the base layer having indentations arranged along a bottom surface proximate the raised portions to improve ventilation and to effectively provide low density cavities in the impact-absorbing layer to control performance (e.g. compression rates) of the raised portions during an impact event.

FIG. 19 shows a cross-sectional view of an impact-absorbing layer having a plurality of raised portions extending from a base layer and a plurality of openings in the base layer to improve ventilation.

FIG. 20 shows an impact-absorbing layer having a plurality of raised portions extending from a base layer.

FIG. 21 shows a top perspective view of an impact-absorbing layer having a plurality of raised portions extending from a base layer, the base layer having a plurality of openings.

FIG. 22 shows a bottom perspective view of an impact-absorbing layer having a plurality of raised portions having a variety of shapes.

FIG. 23 shows a top perspective view of the impact-absorbing layer of FIG. 22 having a plurality of raised portions having a variety of shapes.

FIG. 24 shows a top perspective view of a one-piece impact-absorbing layer adapted to fold and fit within a sports helmet to protect a user from head injuries resulting from rotational acceleration.

FIG. 25 shows a top perspective view of a multi-piece impact-absorbing layer adapted to fit within a sports helmet to protect a user from head injuries resulting from rotational acceleration.

FIG. 26 shows a side view of a multi-piece impact-absorbing layer adapted to fit within a sports helmet to protect a user from head injuries resulting from rotational acceleration.

FIG. 27A shows a side cross-sectional view of a raised portion.

FIG. 27B shows a side view of a raised portion.

FIG. 27C shows a top cross-sectional view of a raised portion.

FIG. 27D shows a top perspective cross-sectional view of a raised portion.

FIG. 28 shows a top perspective cross-sectional view of a raised portion.

FIG. 29 shows a top perspective cross-sectional view of a raised portion with vents passing through a lower portion of the raised portion.

FIG. 30 shows a top perspective view of a raised portion with vents passing through a lower portion of the raised portion.

FIG. 31 shows an impact-absorbing layer having a plurality of raised portions, the raised portions being shaped like columns.

FIG. 32 shows a cross-sectional side view of an impact-absorbing layer having two raised portions extending from a base layer, where a left raised portion has a convex end portion, and a right raised portion has a concave end portion.

FIG. 33 shows two impact absorbing layers similar to the impact-absorbing layer of FIG. 32 where a first impact-absorbing layer is stacked on a second impact-absorbing layer to form a series of pillars.

FIG. 34 shows an impact-absorbing layer having a foam layer positioned between a first polymer layer and a second polymer layer, the first polymer layer having one or more flexible columns extending through the foam layer toward the second layer, and the second polymer layer having one or more flexible columns extending through the foam layer toward the first layer.

FIG. 35 shows an impact-absorbing layer having a foam layer positioned between a first polymer layer and a second polymer layer and one or more flexible columns extending from the first polymer layer to the second polymer layer.

FIG. 36 shows an impact-absorbing layer having a foam layer positioned between a first polymer layer and a second polymer layer and one or more flexible columns extending from the first polymer layer to the second polymer layer.

FIG. 37 shows a suspension system for securing a protective helmet to a player's head, the protective helmet having an impact-absorbing layer that is held proximate an outer shell by an adjustable suspension system.

FIG. 38 shows a helmet with a suspension system for securing the helmet to a person's head.

FIG. 39 shows a helmet with a suspension system for securing the helmet to a person's head.

FIGS. 40A-D show cross-sectional views of an impact-absorbing layer having a first member and a second member, the first member being connected to the second member by a plurality of flexible raised portions that are configured to collapse during an impact event to absorb forces (e.g. perpendicular or tangential) resulting from the impact event.

FIG. 41 shows an attachment feature for securing a fabric layer to an outer shell of a protective helmet to maintain an impact-absorbing layer in a proper position against the outer shell.

FIG. 42 shows the attachment feature of FIG. 41 with a stress distribution feature (e.g. plastic or carbon fiber washer) configured to reduce the likelihood of tearing of the fabric layer, or other portions of the suspension system, near the location of the attachment feature.

FIG. 43 shows an impact-absorbing layer wrapped around an edge of an outer shell and adhered to an exterior surface of the outer shell to facilitate joining of the impact-absorbing layer to the outer shell.

FIG. 44 shows an impact-absorbing layer adhered to an interior surface of an outer shell of a sports helmet to facilitate joining of the impact-absorbing layer to the outer shell.

FIG. 45 shows an impact-absorbing layer having a base layer and flexible raised portions extending from the base layer, the impact-absorbing layer having a plurality of vents to improve ventilation and player comfort (e.g. by reducing the temperature of the player's head).

FIG. 46 shows a sports helmet with a suspension system securely attached to a player's head and provides a partial cutaway view exposing internal features of the sports helmet.

FIG. 47 shows a first impact-absorbing layer having a first base layer and a first plurality of raised portions extending from the first base layer, the first impact-absorbing layer positioned on top of a second impact-absorbing layer having a second base layer and a second plurality of raised portions extending from the second base layer.

FIG. 48 shows an enlarged cross-sectional view of the first and second impact-absorbing layers shown in FIG. 47.

FIGS. 49A-B show visual representations of an experimental test set-up designed to evaluate the performance of the raised portions during an impact event. FIG. 49A shows the test set-up prior to an impact event, and FIG. 49B shows the test set-up during an impact event.

FIG. 50 shows one raised portion from the experimental test set-up of FIG. 49A prior to the impact event, the raised portion includes three horizontal markings that are equally spaced.

FIG. 51 shows one raised portion during the impact event of FIG. 49B, the three horizontal markings serve as indicators as to where the raised portion is experiencing compression and tension forces.

FIG. 52A-B show visual representations of an experimental test set-up designed to evaluate the performance of the raised portions during an impact event. FIG. 52A shows the test set-up prior to an impact event, and FIG. 52B shows the test set-up during an impact event with zones of compression and tension identified within each raised portion.

FIG. 53 shows one raised portion from the experimental test set-up of FIG. 49B during the impact event, the raised portion includes three horizontal markings that are equally spaced, the three horizontal markings serve as indicators as to where the raised portion is experiencing compression and tension forces. A primary compression zone, a secondary compression zone, a stress concentration location, and a location of deflection are identified.

FIG. 54 shows a sports helmet with a suspension system securely attached to a player's head and provides a partial cutaway view exposing internal features of the sports helmet.

DETAILED DESCRIPTION

Rotational acceleration, also known as angular acceleration, is a quantitative expression of a change in angular velocity that a spinning object undergoes per unit time. To protect a player's brain from damage caused by rotational acceleration associated with an impact event (e.g. a collision with another player or the ground), a protective helmet can be configured to ensure that a peak rotational acceleration experienced by the player's head's center of gravity is significantly less than the peak rotational acceleration experienced by the outer shell of the helmet during the impact event. In one example, a sports helmet can include a hard outer shell that, during an impact event, rotates independently from a base layer of an impact-absorbing layer positioned within the helmet. The impact-absorbing layer can include a plurality of flexible raised portions that are configured to topple over as the hard outer shell rotates relative to the impact-absorbing layer. As the flexible raised portions topple over, the duration of the impact event experienced by the player's head is effectively lengthened, thereby reducing the peak rotational acceleration experienced by the player's head's center of gravity and significantly reducing the likelihood of injury occurring to the player's brain. In some examples, the impact-absorbing layer can be captured against an interior surface of the outer shell by a suspension system that allows the hard outer shell to move relative to the impact-absorbing layer during an impact event. In one example, the impact-absorbing layer can be captured between the hard outer shell and an inner fabric layer that snugly conforms to the player's head.

A protective helmet 100 can be any device configured to protect a person's head from injury. The helmet 100 can be used for work, recreation, or special purposes. Examples of recreational helmets include hockey helmets, cycling helmets, skateboard helmets, motorcycle helmets, baseball helmets, and football helmets. Examples of work helmets include hard hats and firefighter helmets. Examples of special purpose helmets include helmets for patients diagnosed with, for example, epilepsy or plagiocephaly.

The helmet 100 can include a hard outer shell 105. In certain recreational helmets, the helmet 100 can include a facemask 110 that is attached to the hard outer shell 105 by one or more fasteners, as shown in FIG. 1. The helmet 100 can include a chin strap 115 that is removably attached to the helmet. The chin strap 115 can aid in securing the helmet 100 to the player's head 150 and prevent the helmet from dislodging from the player's head during an impact event. In some instances, the chin strap 115 can be attached to the hard outer shell 105. In other instances, as shown in FIGS. 37-39, 46, and 54, a chin strap 116 can be attached, by a tensioning strap 145, to an adjustable suspension system 101 that is attached to the outer shell 105 of the helmet 100 by tethers 130. The tethers 130 can be configured to permit a certain amount of rotation of the hard outer shell 105 relative to the player's head 150 during an impact event, as shown in FIG. 3.

FIG. 2 shows a cross-sectional side view of a sports helmet 100. In one example, the helmet 100 can include an impact-absorbing layer 120 captured between an interior surface of the hard outer shell 105 and an inner fabric layer 125. The hard outer shell 105 can be made of any suitable hard material, such as carbon fiber composite or a thermoplastic polymer (e.g. acrylonitrile butadiene styrene). To provide space for impact-absorbing features, the interior volume of the outer shell can be sized to be larger than the player's head. The hard outer shell 105 can be sufficiently rigid to avoid significant inward deflection of the outer shell toward a user's head during an impact event.

The impact-absorbing layer 120 can be made of any suitable material. In one example, the impact-absorbing layer 120 can be made of a polymer, rubber, closed-cell foam, inflatable rubber bladder, vinyl nitrile, urethane foam, or microcellular urethane foam such as, for example, PORON manufactured by Rogers Corporation located in Rogers, Conn. In some instances, the microcellular urethane foam can be manufactured according to one or more processes (e.g. a mechanical frothing process) described in PCT Application No. PCT/JP2012/068593, U.S. Pat. No. 7,718,102, and Canadian Patent No. CA1174412, which are each hereby incorporated by reference in their entirety. The microcellular urethane foam can have an average cell size of about 100-400 μm, 150-300 μm, 100-200 μm, or 150 μm. The microcellular urethane foam can be coated (e.g. in-mold coated) with a continuous skin of, for example, a thermoplastic elastomer (TPE). The thermoplastic coating can prevent bacteria or mold from entering and growing within the foam. Preventing growth of bacteria and mold is desirable in sporting equipment, which is often exposed to moisture and heat, two factors that promote growth of bacteria and mold. To provide additional protection against bacteria growth, the impact-absorbing layer 120 can include an antimicrobial coating such as, for example, antimicrobial coatings manufactured by Microban International, Ltd. located in Huntersville, N.C.

The impact-absorbing layer 120 can include one or more flexible raised portions 135 (e.g. protuberances, pillars, columns) extending therefrom. The one or more flexible raised portions 135 can have any suitable shape that permits the one or more raised portions to fold over during an impact event to lengthen the duration of an impact and reduce the rotational acceleration experienced by the player's head's center of gravity, which is located approximately equidistant between the player's left and right temples. In some examples, the raised portions 135 can resemble cones or tapered pillars and can be defined by a side angle, a top radius, and a bottom radius. The one or more raised portions can serve as impact-absorbing features that occupy a gap between the player's head and an interior surface of the outer shell 105 of the helmet 100. The one or more raised portions 135 can extend from a base layer of the impact-absorbing layer 120 outwardly toward an interior surface of the outer shell 105. The flexible raised portions 135 can have ends that contact the interior surface of the hard outer shell 105, as shown in FIG. 2. When a player is involved in a collision, the hard outer shell 105 of the sports helmet 100 can rotate relative to the player's head 150, as shown in FIG. 3. As a result of the relative motion of the outer shell 105 with respect to the player's head 150, the raised portions 135 fold over. Since the raised portions 135 are upright in their resting state (see, e.g. FIG. 2) and, consequently, resist folding over, a certain amount of force must be applied to each raised portion 135 to cause it to fold over (see, e.g. FIG. 3). The amount of force required to fold over a raised portion 135 (either partially or fully) is determined, at least in part, by its material properties, base radius, top radius, side angle, and height. The process of folding over the raised portions 135 increases the duration of the impact event, resulting in a lower peak rotational acceleration being experienced by the player's head's center of gravity.

FIG. 4 shows a raised portion 135 having several measurements that define the size, shape, mass, and performance of the raised portion 135. The raised portion 135 can have a side angle (θ) measured with respect to a centerline 400 of the raised portion, a thickness (t) of a base layer 140, a height (h) of the raised portion measured from the base layer, a base radius (R₁) measured where the base of the raised portion 135 meets the base layer 140, and a top radius (R₂) measured at the top end of the raised portion. The raised portion 135 can be made of a first material having a first density (ρ₁), and the base layer 140 can be made of a second material having a second density (ρ₂). In some examples, the first and second materials can be the same material, and ρ₁ and ρ₂ can be equal or approximately equal. In other examples, the first and second materials can be different materials, and ρ₁ can be greater than or less than ρ₂, depending on the desired performance characteristics of the raised portion 135 and base layer 140. The variables (θ, t, h, R₁, R₂, ρ₁, ρ₂) that define the raised portion 135 and base layer 140 can be selected to provide desired performance characteristics of the raised portion and the base layer to suit a particular use such as, for example, in an impact-absorbing layer 120 of a helmet 100 worn by a quarterback in a football game. The variables selected for the raised portion 135 and the base layer 140 can be different for the quarterback (e.g. who experiences infrequent, large impact events) than for an offensive lineman (e.g. who experiences frequent, small impact events).

FIGS. 5-23 show impact-absorbing layers 120 having raised portions 135 extending from a base layer 140. The various impact-absorbing layers 120 have a variety of side angles (θ) measured with respect to a centerline 400 of the raised portion, thicknesses (t) of the base layer 140, heights (h) of the raised portions measured from the base layer, base radii (R₁) measured where the base of the raised portion meets the base layer, and top radii (R₂) measured at the top end of the raised portion. Modifying the physical geometry of the raised portions 135 can influence the amount of energy that is required to partially or fully fold over the raised portions. The physical geometry and material properties of each raised portion 135 can determine how much energy will be absorbed through the process of folding over each raised portion (e.g. due to stretching and compressing zones of each raised portion 135, as shown in FIG. 53). For instance, a raised portion 135 with a small base radius R₁ will topple more easily than a raised portion with a large base radius R₁. Likewise, a raised portion 135 with a small side angle (θ) will topple more easily than a raised portion with a large side angle (θ). The rate at which the raised portions 135 topple will dictate how tightly or loosely coupled the rotational acceleration of the hard outer shell 105 is to the rotational acceleration of the player's head's center of gravity.

To dissipate frequent, small impact events, such as those experienced by an offensive lineman in a football game (e.g. upon engaging an opposing defensive lineman), it can be desirable to provide raised portions 135 that are configured to topple quite easily, thereby effectively dissipating the harmful impact forces the player is most likely to encounter during the game. To dissipate infrequent, large impact events, such as those experienced by a quarterback in a football game (e.g. during a sack), it can be desirable to provide raised portions 135 that are configured to resist toppling during small impact events and, rather, to topple during large impact events, thereby effectively dissipating the harmful impact forces the quarterback is most likely to encounter during the game.

The impact-absorbing layer 120 can have two or more base layers 140 made of materials having differing densities. The two or more base layers 140 can be made of similar or dissimilar materials. The two or more base layers 140 can be arranged in a stacked configuration and can be joined by any suitable manufacturing or joining process or processes (e.g. casting, injection molding, blow molding, gluing, stitching, etc.). As shown in FIG. 12, the impact-absorbing layer 120 can have a first base layer 140 and a second base layer 170 where the second base layer has a density greater than the density of the first base layer. For instance, the first base layer 140 can be formed from a foam material having a density of 1-20 pounds per cubic foot, and the second base layer 170 can be formed from a material having a density that is at least 5-15%, 10-20%, 15-35%, 30-50%, 45-75% or more greater than the density of the first base layer. In another example, the impact-absorbing layer 120 can have a first base layer 140 and a second base layer 170 where the second base layer has a density less than the density of the first base layer. For instance, the second base layer 170 can be formed from a foam material having a density of 1-20 pounds per cubic foot, and the first base layer 140 can be formed from a material having a density that is at least 5-15%, 10-20%, 15-35%, 30-50%, 45-75% or more greater than the density of the second base layer. The selection of densities for the first and second base layers (140, 170) can be determined, at least in part, by desired performance attributes of a resulting product (e.g. sports helmet 100).

The relative spacing of the raised portions 135 can be adjusted to alter the performance of the impact-absorbing layer 120. For instance, the raised portions 135 can be closely spaced, as shown in FIG. 17, to provide a greater cumulative resistance against the raised portions folding over. Alternately, the raised portions 135 can be relatively widely spaced, as shown in FIG. 14, to reduce material costs and to provide a lower cumulative resistance to the raised portions folding over. The impact-absorbing layer 120 shown in FIG. 14 may be suitable to protect a player from frequent, small impact forces, and the impact-absorbing layer 120 shown in FIG. 17 may be suitable to protect a player from infrequent, large impact forces.

It can be desirable to select a physical geometry and material properties of the raised portions based on the intended use of the impact-absorbing layer 120. For instance, in a sports helmet for a child playing in a youth league where only minor collisions are expected, it can be desirable to have the raised portions 135 fold over relatively easily. In a sports helmet for an adult playing in a professional league where major collisions are expected, it can be desirable to have the raised portions 135 be more difficult to fold over. In other situations, the behavior of the raised portions 135 can be tailored for a particular individual or position (e.g. lineman, running back, quarterback, etc.). For an offensive lineman who experiences a series of minor collisions per game, it can be desirable to have the raised portions 135 fold over relatively easily to ensure that a significant percentage of each small impact is absorbed by the process of folding over the raised portions. This can help prevent brain injuries caused by the cumulative effect of numerous minor impacts over the course of the player's career. Once the raised portion 135 has fully toppled, it may no longer be capable of absorbing impact energy or reducing the peak rotational acceleration experienced at the player's head's center of gravity. Therefore, for a running back who experiences a series of major collisions per game, it can be desirable to have the raised portions 135 be more difficult to fold over to ensure that a significant percentage of each major impact is absorbed by the process of folding over the raised portions 135. In some applications, it can be desirable to select a geometry based on the type of impacts a certain player will likely experience during a game based on, for example, historical data collected during one or more prior games. For example, data (e.g. linear acceleration data, rotational acceleration data, impact duration data, or impact location data) can be collected from one or more accelerometers or sensors attached to the outer shell 105 of the helmet or imbedded in the impact-absorbing layer 120 of the helmet. In some instances, the accelerometers can be attached directly to the player's head such as, for example, by inserting the accelerometers into the player's ear (e.g. in a housing similar to a hearing aid). Data produced by the accelerometer can be stored locally on a computer readable medium or transmitted to a remote location (e.g. a computer located near the sidelines). In one example, the helmet can incorporate a Head Impact Telemetry (HIT) system developed by Simbex LLC of Lebanon, N.H. The HIT system can include six spring-mounted accelerometers and an antenna that transmits data via radio frequency to a sideline receiver and computer system.

The impact-absorbing layer 120 can include openings to improve ventilation and comfort for the player. The vents 180 can pass through the impact-absorbing layer 120. The vents 180 can be located in the base layer 140 between raised portions 135, as shown in FIG. 19. Alternately, the vents 180 can be located within the raised portions 135, as shown in FIGS. 21 and 27-30. One or more vents 180 can be positioned in the raised portions 135 to reduce the amount of force that is required to topple the raised portion and to influence the direction in which the raised portion topples when the hard outer shell 105 is subjected to a tangential force. For example, the raised portions 135 shown in FIG. 21 are likely to topple in one of four directions due to the location of the vents 180 near the base of each raised portion.

FIG. 18 shows an impact-absorbing layer 120 having a plurality of raised portions 135 extending from a base layer 140. The base layer 140 can include one or more indentations 175 arranged along a bottom surface of the base layer proximate the raised portions to improve ventilation. The indentations 175 can effectively serve as low density (e.g. zero density) cavities in the impact-absorbing layer 120 to modify performance (e.g. compression rates) of the raised portions 135 during an impact event. For instance, during an impact event, an indentation 175 positioned beneath a raised portion 135, as shown in FIG. 18, can result in a rapid initial compression rate when a force (F) is initially applied to the raised portion, and the raised portion 135 is pressed downward and fills the void of the indentation 175. Then, once the void of the indentation 175 is filled, the compression rate decreases significantly as the raised portion 135 begins compressing into itself. Accordingly, the placement and size of the indentations 175 can be used to influence the compression rate profile of the impact-absorbing layer 120.

The hard outer shell 105 of the helmet 100 can include openings that correspond to vents 180 in the impact-absorbing layer 120 to improve convective heat transfer away from the player's head. In another example, indentations 175 can be formed in the impact-absorbing layer 120 to permit air flow between the player's head and the impact-absorbing layer. The indentations 175 can also serve as passageways for perspiration to escape.

FIGS. 22 and 23 show an impact-absorbing layer 120 having raised portions 135 with a variety of shapes, including conical 235, tiered 240, and multi-faceted 245 shapes. An impact-absorbing layer 120 for used in a sports helmet 100 can have raised portions 135 with one or more of the shapes shown in FIGS. 22 and 23.

As shown in FIG. 23, several of the raised portions 135 have additional support members 230 positioned where the raised portion meets the base layer 140. The support members 230 can increase the amount of force required to topple the raised portion 135. The support members 230 can increase the durability of the raised portion 135 and improve life expectancy before failure (e.g. by preventing tearing or separation of the raised portion 135 from the base layer 140). As shown in FIG. 22, the raised portions 135 can be solid, hollow, or a combination thereof.

The raised portions 135 can extend from a top surface of the base layer 140, as shown in FIG. 23 or from the bottom surface of the base layer, as shown in FIG. 22. Each downward-extending raised portion 250 can be positioned directly underneath an upward-extending raised portion 135.

FIG. 24 shows a one-piece impact-absorbing layer 120 that can be incorporated into a sports helmet 100. The one-piece impact-absorbing layer 120 is shown in a planar orientation prior to installation within the hard outer shell 105 of the sports helmet 100. The raised portions 135 extending from the impact-absorbing layer 120 can have uniform size, shape, and/or spacing, as shown in FIG. 24. In another example, the raised portions 135 can vary in size, shape, and/or spacing depending on their location within the helmet 100. The impact-absorbing layer 120 shown in FIG. 24 can be manufactured with positive draft on its top surfaces to permit the impact-absorbing layer 120 to be easily removed from a mold (e.g. ejected out of the mold).

FIGS. 25 and 26 show multiple impact-absorbing layers 120 prior to installation in a sports helmet 100, in locations near where they will eventually be installed within the hard outer shell 105 of the sports helmet 100. The multiple impact-absorbing layers 120 can form a multiple-piece impact-absorbing layer for a sports helmet 100. The raised portions 135 on each impact-absorbing layer 120 can be tailored based on installation location. For instance, the raised portions 135 located near the front of the helmet 100 can be constructed from a denser material than the raised portions located near the rear of the helmet.

In many sports, front impacts can be severe. It can be desirable to provide raised portions 135 constructed from a dense material to ensure the raised portions can adequately dissipate forces without completely compressing and becoming nonfunctional during a severe front impact.

The geometry of the human head 150 and the fit of the helmet 100 can influence material selection for the raised portions 135 of the impact-absorbing layer 120. For instance, since a player's face is typically exposed around their eyes to permit an unobstructed view of the playing field, the forehead area is typically the only surface on the front of the player's head where an impact-absorbing layer 120 can be placed. Because the forehead area has a much smaller surface area compared to the side or rear surfaces of the player's head, the raised portions 135 located near the front of the helmet 100 may need to be constructed from a denser foam to ensure they are capable of withstanding high impact forces without completely compressing and becoming nonfunctional.

FIGS. 27-30 show various views of a raised portion 135 with vents 180 passing through a lower portion of the raised portion. The vents 180 can influence the amount of force required to fold over the raised portion 135 during an impact event. The vents 180 can also serve as air passageways that allow air to escape from a cavity located beneath the raised portion 135 when the raised portion is pressed downward during an impact event. As the raised portion 135 rebounds and expands after an impact event, air is drawn back into the cavity through the vent 180. As a result of air being pumped into and out of the cavity through the vent 180, the player experiences cooling, which can improve comfort and prevent issues relating to overheating (e.g. heat exhaustion).

FIG. 31 shows an impact-absorbing layer where the raised portions 135 are cylindrically shaped. The raised portions 135 can be an integrally formed part of the impact-absorbing layer or can be attached to the base layer 140 with an adhesive or by any other suitable joining process. When a cylindrical raised portion 135 is folded over, it may result in a stress concentration forming near the location where the raised portion meets the base layer 140. Repeated folding may eventually result in tearing near the location of the stress concentration, which would necessitate replacement of the impact-absorbing layer. To avoid this outcome, it can be desirable to include a base radius (R₁) where the raised portion meets the base layer 140, as shown in FIGS. 5-20. FIG. 5 shows a relatively small base radius (R₁), and FIG. 10 shows a relatively large base radius (R₁).

FIG. 32 shows a portion of an impact-absorbing layer 120 having two raised portions 135 extending from a base layer 140. The leftmost raised portion 135 has a convex end 3205, and the rightmost raised portion has a concave end 3210. In one example, the concave end 3310 of the raised portion can be configured to receive a protrusion extending from the interior surface of the hard outer shell 105 to effectively connect the impact-absorbing layer 120 to the hard outer shell. In another example shown in FIG. 33, a first impact absorbing layer 120 can be stacked on a second impact-absorbing layer 121 that is rotated 180 degrees with respect to the first impact-absorbing layer 120. Each convex end 3205 can be inserted into a concave end 3210 to form a series of pillars between a first base layer 140 and a second base layer 141. In some instances, an adhesive layer may be added to one or both of the convex and concave ends to provide permanent or semi-permanent attachment.

FIG. 34 shows an impact-absorbing layer 3400 for a sports helmet 100. The impact-absorbing layer 3400 can include a top layer 3410 and a bottom layer 3405. The top layer 3405 can slide relative to the bottom layer 3410 to absorb impact energy during an impact event and effectively reduce the magnitude of rotational acceleration experienced by the player's head's center of gravity. The top layer 3410 can include one or more 3415 resilient spring members that are relatively stiff but are capable of compressing (e.g. by bending near an elbow location) against the bottom layer 3405 during an impact event to absorb impact energy. Likewise, the bottom layer 3405 can include one or more 3420 resilient spring members that are relatively stiff but are capable of compressing (e.g. by bending near an elbow location) against the top layer 3410 during an impact event to absorb impact energy. The top layer 3410 can include a layer of impact absorbing foam 3425 (e.g. microcellular urethane foam). Likewise, the bottom layer 3405 can include a layer of impact-absorbing foam 3430 (e.g. microcellular urethane foam). During an impact event, the impact-absorbing foam (e.g. 3425, 3430) may be compressed. The impact-absorbing foam (e.g. 3425, 3430) may rebound relatively slowly after being compressed, so the foam may not have enough time to fully expand (i.e. recover) before a second impact event occurs. The resilient spring members (e.g. 3415, 3420) can be made of a material (e.g. such as a thermoset plastic) that recovers relatively quickly from an impact event that has resulted in compression or bending of the resilient spring members. Therefore, despite the impact-absorbing foam (e.g. 3425, 3430) being partially compressed, the resilient spring members (e.g. 3415, 3420) will already be fully expanded and will provide adequate separation between the first and second layers (3405, 3410) to allow the first and second layers to slide relative to each other to reduce the peak acceleration experienced by the bottom layer 3405 compared to the top layer 3410. In addition, the resilient spring members will be capable of absorbing impact energy from the second impact event. In this way, the impact-absorbing layer 3400 is aided by having two types of impact-absorbing structures disposed therein, the first being a faster reacting structure and the second being a slower reacting structure. The response rate of both the first and second structures can be altered by adjusting the material properties and geometries of the structures.

In one example, the top layer 3410 of the impact-absorbing layer 3400 in FIG. 34 can adhere to an inner surface of the hard outer shell 105 of the sports helmet 100. The bottom layer 3405 can directly contact a player's head or can contact an inner fabric layer 125 that contacts the player's head. In another example, the outer surface of the top layer 3410 can be the hard outer shell 105, and the resilient spring members 3415 can extend inward from an inner surface of the hard outer shell 105.

FIG. 35 shows an impact-absorbing layer 3500 having a top member 3510 and a bottom member 3505. The impact-absorbing layer 3500 can include an impact-absorbing material (e.g. microcellular urethane foam) 3515 disposed between the top member 3510 and the bottom member 3505. The impact-absorbing layer 3500 can be configured to permit some lateral movement of the top member 3510 relative to the bottom member 3505. The impact-absorbing layer 3500 can include one or more resilient spring members 3520 extending from the top member 3510 to the bottom member 3505. The resilient spring member 3520 can be nonlinear and can be made of a material (e.g. such as a thermoset plastic) that recovers relatively quickly from an impact event resulting in compression or bending of the resilient spring member. The response rate of the resilient spring member 3520 can be altered by adjusting its material properties and geometry. For instance, the thickness of the resilient spring member 3520 can be increased to increase the force required to compress the spring during major collisions. In another example, the elasticity of the resilient spring member 3520 can be increased to permit greater relative rotation between the top member 3510 and the bottom member 3505 during an impact event.

FIG. 36 shows an impact-absorbing layer 3600 having a top member 3610 and a bottom member 3605. The impact-absorbing layer 3600 can include an impact-absorbing material (e.g. microcellular urethane foam) 3615 disposed between the top member 3610 and the bottom member 3605. The impact-absorbing layer 3600 can be configured to permit lateral movement of the top member 3610 relative to the bottom member 3605. The impact-absorbing layer 3600 can include one or more resilient spring members 3620 extending from the top member 3610 to the bottom member 3605. The resilient spring members 3620 can be nonlinear and can be made of a material (e.g. such as a thermoset plastic) that recovers relatively quickly from an impact event resulting in compression or bending of the resilient spring member. The response rate of the resilient spring member 3620 can be altered by adjusting the material properties and geometry of member. For instance, the thickness of the resilient spring member 3620 can be increased to increase the force required to compress the spring to provide impact protection during major collisions.

FIG. 37 shows a sports helmet 100 with an adjustable suspension system 101 configured to attach a hard outer shell 105 of the sports helmet 100 securely but movably to a player's head 150. The suspension system 101 can include a first fabric portion 125 that fits around a front portion of the player's head 150. The suspension system 101 can include a second fabric portion 3126 that fits around a rear portion of the player's head 150. The fabric portions (125, 126) can be made of any suitable natural or synthetic fibers arranged to form a fabric, webbing, or netting. In some examples, the fabric portions (125, 126) can be a durable, breathable, mesh or spandex material. In another example, the fabric portions can be a polymer-based net-like material. The first fabric portion 125 can be flexibly attached to the outer shell 105 of the sports helmet 100 by a first tether 130. Likewise, the second fabric portion 126 can be flexibly attached to the outer shell 105 of the sports helmet 100 at a second tether 130.

As shown in FIG. 37, where the first and second fabric portions (125, 126) meet along the side of the player's head, a tensioning strap 145 can be attached. The tensioning strap 145 can extend from a first attachment point to a chin cup 116. Once the helmet 100 is fitted onto the player's head 150 and the chin cup 116 is fitted over the player's chin, tightening the tensioning strap 145 will simultaneously draw the first fabric portion 125 tight against the player's forehead, the second fabric portion 126 tight against the back of the player's head, and the chin cup 116 tight against the player's chin to securely attach the helmet to the player's head 150 by applying pressure at three surfaces of the player's head (i.e. forehead, back of the head, and chin).

As shown in FIG. 37, a first impact-absorbing layer 120 can be positioned between an interior surface of the outer shell 105 and the first fabric portion 125. A second impact-absorbing layer 121 can be positioned between the interior surface of the outer shell 105 and the second fabric portion 126. The impact-absorbing layers (120, 121) can each include a plurality of flexible raised portions 135 extending from a base layer 140, and the impact-absorbing layers (120, 121) can be oriented with the flexible raised portions 135 extending outwardly toward the hard outer shell 105 of the sports helmet 100 with the base layers 140 proximate the player's head 150. The impact-absorbing layers (120, 121) can be made of any suitable impact-absorbing material, such as microcellular urethane foam.

During a front impact event (e.g. a collision with another player), the adjustable suspension system 101 allows the outer shell 105 of the sports helmet 100 to rotate relative to the player's head, as shown in FIG. 3 (e.g. forward, backward, or sideways depending on the nature of the collision). As the outer shell 105 rotates relative to the player's head 150, friction between an interior surface of the outer shell 105 and the flexible raised portions 135 will cause the flexible raised portions to fold over (i.e. topple over), thereby absorbing and dissipating a percentage of impact energy, increasing the duration of the impact event, and reducing the peak rotational acceleration experienced by the player's head's center of gravity. Consequently, the peak rotational acceleration experienced by the player's brain is significantly less than it would have been with a traditional helmet having padding that is statically attached to an outer shell.

In some examples, the first fabric layer 125 and the second fabric layer 126 shown in FIG. 37 can be replaced with a single fabric layer where the tensioning strap 145 is attached to the fabric layer near a player's right temple and left temple. Specifically, the first and second fabric layers (125, 126) can be replaced with a single fabric layer having an opening or attachment feature near the player's right temple and left temple to facilitate attachment of the tensioning strap 145 to the fabric layer.

FIG. 38 shows a protective helmet 100 with an adjustable suspension system 101 configured to attach the helmet securely but movably to the player's head 150. The suspension system 101 can include two or more upper tensioning straps 146, where each upper tensioning strap is configured to wrap around at least a portion of the player's head to securely attach the sports helmet to the player's head. The suspension system 101 can include a fabric portion 125 extending between the two upper tensioning straps 146. The fabric portion 125 can fit snuggly around a rear portion of the player's head 150, thereby distributing a force applied by the suspension system 101 (e.g. when tightening the suspension system 101 during fitting of the helmet 100) to a larger area of the player's head, thereby avoiding pressure points and improving comfort. A lower tension strap 147 can extend around the player's forehead and around a back side of the player's head near the player's neck. The lower tension strap 147 can attach to the upper tension strap 146 at a left side junction 160 and a right side junction 160 located along the left and right sides of the player's head 150, respectively. A tensioning strap 145 can extend from the left side junction 160 to the right side junction 160 and can include a chin cup 116 configured to fit snugly against the player's chin. Tightening the tensioning strap 145 can draw the fabric portion 125 snugly against the back and top surfaces of the player's head and can draw the chin cup 116 snugly against the player's chin. Once tightened, the suspension system 101 remains approximately stationary with respect to the player's head 150, while the hard outer shell 105 remains rotatable relative to the player's head thereby allowing for dissipation of impact forces by the impact-absorbing layer 120 positioned between the hard outer shell 105 and the player's head 150.

The suspension system 101 shown in FIG. 38 can include at least one tether 130 connecting each upper tensioning strap 146 to the outer shell 105 of the helmet 100. Once the helmet 100 is fitted onto the player's head 150 and the chin cup 116 is fitted over the player's chin, tightening the tensioning strap 145 will simultaneously draw the fabric portion 125 tight against the back of the player's head, the one or more upper and lower tensioning straps (146, 147) tight against the player's head, and the chin cup 116 tight against the player's chin to securely but moveably attach the protective helmet 100 to the player's head 150. The helmet 100 can include an impact-absorbing layer 120 positioned between the player's head 150 and the interior surface of the outer shell 105. As shown in FIG. 38, the impact-absorbing layer 120 can be arranged with a plurality of raised portions 135 extending outward toward an interior surface of the hard outer shell 105. The impact-absorbing layer 120 can be any of the impact-absorbing layers described herein.

FIG. 39 shows a protective helmet 100 with a suspension system 101 configured to attach the helmet securely and movably to a player's head 150. The suspension system 101 can include one or more rear tensioning straps 148 that engage a front tensioning strap 149 near a junction 160 along the side of the player's head 150. The suspension system 101 can include a fabric portion 125 that extends from a first rear tensioning strap 148 to a second rear tensioning strap 148. The fabric portion 125 can cover and cradle a rear portion of the player's head 150. The front tensioning strap 149 can extend from a player's forehead, through the junction 160 and down to a chin cup 116 that fits over the player's chin. After the sports helmet 100 is fitted onto the player's head 150 and the chin cup 3920 is fitted over the player's chin, tightening the front tensioning strap 149 will simultaneously draw the fabric portion 126 tight against the back of the player's head, the rear suspension straps 148 tight against the player's head, and the chin cup 116 tight against the player's chin to securely but moveably attach the protective helmet 100 to the player's head 150. The helmet 100 can include an impact-absorbing layer 120 positioned between the player's head 150 and the interior surface of the hard outer shell 105 and between the fabric portion 125 and the interior surface of the hard outer shell 105. As shown in FIG. 39, the raised portions 135 of the impact-absorbing layer 120 can extend outward toward an inner surface of the hard outer shell 105. The impact-absorbing layer 120 can be any of the impact-absorbing layers described herein.

FIG. 40A-D show an impact-absorbing layers 120 having a top member 4005, a bottom member 4010, and two or more flexible resilient members 4015 extending from the top member to the bottom member. The flexible resilient members 4015 can resemble columns having uniform thickness, such as those shown in FIGS. 40A, 40C, and 40D. Alternately, the flexible resilient members 4015 can resemble tapered columns having varying thickness, as show in FIG. 40B. FIG. 40A shows an impact-absorbing layer 120 with no force applied, and FIG. 40C shows the same impact-absorbing layer 120 with a perpendicular force being applied. In response to the perpendicular force, the flexible resilient members 4015 buckle or compress, thereby absorbing impact energy (i.e. converting kinetic energy into heat and potential energy stored in the compressed flexible resilient members 4015). FIG. 40D shows an impact-absorbing layer 120 with a tangential force being applied. In response to the tangential force, the flexible resilient members 4015 fold over (i.e. compressing in certain zones and stretching in certain zones), thereby absorbing and dissipating impact energy.

FIG. 41 shows an attachment feature 4105 for securing an impact-absorbing layer 120 within a sports helmet 100. The sports helmet 100 can include a liner 125 (e.g. a fabric liner), and the impact-absorbing layer 120 can be captured between the liner 4110 and an interior surface of an outer shell 105 of the sports helmet 100. The attachment feature 4105 can be a rubber grommet or other suitable fastener (e.g. stainless steel screw) that is configured to attach to the outer shell 105 of the helmet. For instance, the fastener 4105 can be inserted into an opening 4115 in the outer shell 105 of the helmet. The fastener 4105 can trap the liner 4110 against the outer shell, thereby creating a slight compressive force against the impact-absorbing layer 120, which serves to keep the impact-absorbing layer 120 in a proper position within the helmet. As shown in FIG. 42, a shaped washer 4120 (e.g. a plastic or rubber washer) can be used to distribute force over a larger area of the liner (or other portion of the suspension system 101) to prevent the liner 125 from tearing free of the attachment feature 4105 and causing the suspension system 101 to fully or partially detach from the interior surface of the outer shell 105. The shaped washer 4120 can be captured against the liner 125 by the attachment feature 4105.

The impact-absorbing layer 120 can be attached to the outer shell 105 of the sports helmet 100 by any suitable method of attachment (e.g. snaps, glue, adhesive tape, VELCRO, rivets, etc.). FIG. 43 shows an impact-absorbing layer 120 wrapped around an edge of an outer shell 105 of a sports helmet 100 and adhered to an exterior surface of the outer shell to facilitate joining of the impact-absorbing layer 120 to the hard outer shell 105. FIG. 44 shows an impact-absorbing layer 120 adhered to an interior surface of an outer shell 105 of a sports helmet 100 to facilitate joining of the impact-absorbing layer to the hard outer shell.

FIG. 45 shows an impact-absorbing layer 120 having a base layer 140 and flexible raised portions 135 extending from the base layer. The impact-absorbing layer 120 can include a plurality of vents 180 to improve ventilation. Improved ventilation can result in improved player comfort as well as improved safety, by reducing the likelihood of overheating. The base layer 140 can include indentations 175 to provide ventilation along the bottom surface of the impact-absorbing layer 120. In one example, the vent 180 can pass through the impact-absorbing layer 120 and terminate at the indentation 175, thereby providing an air passageway from the indentation to the top surface of the impact-absorbing layer 120 to allow heat and perspiration to escape from the player's head.

FIG. 46 shows a sports helmet 100 with a suspension system 101 for securely and moveably attaching the sports helmet to a player's head 150. The suspension system 101 can include a liner 125 that is configured to conform to the shape of the player's head 150 when a first and second tensioning strap (4610, 4615) are drawn tight after the player places the helmet on his/her head and places a chip cup 4605 over his/her chin. The liner 125 can be made of any suitable material, such as a breathable fabric, and can include openings 4625 through which the first and second tensioning straps (4610, 4615) are threaded. In one example, the first and second tensioning straps can be a single strap. The helmet 100 depicted in FIG. 46 shows a cutaway view revealing a left side of the suspension system 101. The helmet 100 can include a right side of the suspension system that is a mirror image of the left side of the suspension system. As shown in FIG. 46, the helmet 100 can include an impact-absorbing layer 120 located between an interior surface of the hard outer shell 105 and the liner 125. The impact-absorbing layer 120 can include a plurality of raised portions 135 extending outward from a base layer 140 toward an inner surface of the hard outer shell 105.

FIG. 47 shows a first impact-absorbing layer 120 having a first base layer 140 and one or more raised portions 135 extending from the first base layer. The first impact-absorbing layer 120 can be positioned on top of a second impact-absorbing layer 121 having a second base layer 141 and one or more raised portions extending from the second base layer 136. FIG. 48 shows an enlarged cross-sectional view of the impact-absorbing layers (120, 121) shown in FIG. 47. The combination of the first and second impact-absorbing layers (120, 121) can be inserted into the sports helmet 100 and arranged with the base layer 140 of the first impact-absorbing layer 120 positioned against the interior surface of the outer shell 105. In one example, the first and second impact-absorbing layers (120,121) can be constructed from the same material. In another example, the first impact-absorbing layer 120 can be made of a denser material than the second impact-absorbing layer 121. In yet another example, the first impact-absorbing layer 120 can be made of a less dense material than the second impact-absorbing layer 121.

FIGS. 49A-B show visual representations of an experimental test set-up designed to evaluate the performance of an impact-absorbing layer 120 during an impact event. The test set-up consists of a plate 4900 placed on top of the impact-absorbing layer 120. The plate 4900 simulates a hard outer shell 105 of a sports helmet 100. To simulate a collision on the playing field, a steel ball 4905 was dropped at an angle onto the plate 4900, and the performance of the impact-absorbing layer 120 was observed using a high-speed camera and quantified using a data acquisition system. FIG. 49A shows the test set-up prior to the steel ball 4905 being dropped, and FIG. 49B shows the test set-up as the steel ball is striking the plate 4900. When the steel ball 4905 strikes the plate 4900, the raised portions 135 fold over and effectively change the kinetic energy imparted by the steel ball into heat, sound energy, and potential energy, which is later released as the compressed raised portions 135 expand back to their original shape.

FIG. 50 shows one raised portion 135 from the experimental test set-up of FIG. 49A prior to the impact event, where the raised portion includes three horizontal markings that are equally spaced. FIG. 51 shows one raised portion 135 during the impact event of FIG. 49B. In FIG. 51, the three horizontal markings serve as indicators as to where the raised portion is experiencing compression and tension forces. Specifically, the left side of the raised portion is experiencing compression forces, and the right side is experiencing tension forces, including a stress concentration located at the base radius R₁.

FIG. 52A-B show visual representations of an experimental test set-up designed to evaluate the performance of the raised portions 135 during an impact event. FIG. 52A shows the test set-up prior to an impact event, and FIG. 52B shows the test set-up during an impact event with zones of compression (X) and zones of tension (Y) identified within each raised portion 135.

FIG. 53 shows one raised portion 135 from the experimental test set-up of FIG. 49B during the impact event. The raised portion 135 includes three markings that were horizontal and equally spaced prior to impact. The three horizontal markings serve as indicators as to where the raised portion is experiencing compression and tension forces. A primary compression zone 5305, a secondary compression zone 5310, a stress concentration at the base radius 5315, and a location of deflection 5320 are identified. These various instances of deformation of the raised portion 135 during the impact event can effectively convert kinetic energy imparted by the impact event into heat, sound energy, and potential energy, which is later released as the compressed and deformed raised portion 135 expands back to its original shape after the impact event has occurred.

FIG. 54 shows a sports helmet 100 with an adjustable suspension system 101 for securely and moveably attaching the sports helmet to a player's head 150. The adjustable suspension system 101 can include a liner 125 that is configured to conform to the shape of the player's head 150 when a tensioning strap 145 is drawn tight after the player places the helmet 100 on his/her head and places a chip cup 116 over his/her chin. The liner 125 can be made of any suitable material, such as a breathable fabric, and can include an opening 165 located along the side of the player's head through which the tensioning strap 145 is threaded. In one example, the adjustable suspension system 101 can include a tensioning strap 145 that extends from the chin cup 115 through a first opening in the liner 125 located along a left side of the player's head 150, around a back side surface of the player's head, through a second opening in the liner located along a right side of the player's head 150, and back to the chin cup 116.

The helmet 100 depicted in FIG. 54 shows a cutaway view revealing a left side of the suspension system. The helmet 100 can include a right side of the suspension system 101 that is a mirror image of the left side of the suspension system. As shown in FIG. 54, the helmet 100 can include an impact-absorbing layer 120 positioned between an interior surface of the outer shell 105 and the liner 125. In one example, the helmet 100 can include an impact-absorbing layer 121 affixed to the interior surface of the outer shell 105 and oriented with the raised portions 135 facing inward toward the player's head, as shown in FIG. 54, to cushion a rear side of the players head.

Experimental testing was performed on several sports helmets 100 having impact-absorbing layers 120 as described herein. Tests involving front, side, and back impacts were conducted. During the tests, an impactor having a mass of 14 kg was directed at the individual sports helmets at a velocity of 7.6 m/s. The severity of the impacts is evaluated with several criteria, including Head Injury Criteria (HIC), Severity Index (SI), Peak Angular Acceleration, Peak Resultant Upper Neck Load, and Peak Resultant Upper Neck Moment. Head Injury Criterion (HIC) is a measure of the likelihood of a head injury arising from an impact. The HIC can be used to assess safety related to vehicles, personal protective gear, and sports equipment. HIC is typically derived from the acceleration data recovered from an accelerometer mounted at the center of gravity of a dummy's head when exposed to an impact event. HIC is defined as:

${HIC} = \left\{ {\left\lbrack {\frac{1}{t_{2} - t_{1}}{\int_{t_{1}}^{t\; 2}{{a(t)}\ {t}}}} \right\rbrack^{2.5}\left( {t_{2} - t_{1}} \right)} \right\}_{\max}$

where t₁ and t₂ are the initial and final times (in seconds) of the interval during which HIC attains a maximum value.

In the example of a sports helmet 100, the surface finish on the interior surface of the outer shell 105 can influence the coupling efficiency between the interior surface and the raised portions 135 of the impact-absorbing layer 120 during an impact event. For instance, if the interior surface has a relatively high coefficient of friction, the raised portions 135 are likely to begin folding over as soon as the outer shell 105 begins to rotate. Alternately, if the interior surface has a relatively low coefficient of friction, the raised portions 135 are likely to slide along the interior surface of the outer shell 105 for a distance before beginning to fold over as the outer shell begins to rotate. To ensure high coupling efficiency between the outer shell 105 and the raised portions, the interior surface of the outer shell 105 can include recesses (e.g. dimples, pockets), each configured to receive a raised portion. By capturing the raised portions 135 in corresponding recesses in the outer shell 105, the raised portions will be encouraged to begin folding over as soon as the outer shell begins rotating relative to the player's head.

The impact-absorbing layer 120 and suspension systems described herein can be applied to any helmet, including football, hockey, construction, skiing, cycling, skateboarding, baseball, and motorcycle helmets. It can also be applied to other forms of headwear, including hats, boxing headgear, or as a standalone product with the raised portions 135 facing inward or outward from the user's head.

The impact-absorbing layer 120 described herein can be used in a wide variety of applications, including, for example, shoe insoles, medical helmets for infants, backing for ballistic-resistant inserts, shipping materials, image stabilization, and vibration dampening (e.g. in domestic appliances, cameras, precision measuring instruments, electronic equipment, exercise equipment, and vehicle components). Specific examples of sizes and shapes of impact-absorbing layers 120 for sports helmets are described herein. The size and shape of the impact-absorbing layer 120 can be scaled up or down to accommodate the various applications described in this paragraph as well as a wide variety of other applications.

Flexible convoluted foam is commonly used in a wide variety of cases designed for guns, knives, swords, precision tools, collectibles, etc. In such cases, convoluted foam is often used to line the inner surfaces of a hard-shell case to provide protection and support to the contents of the case. The impact-absorbing layer 120 described herein can replace convoluted foam in any of these applications. The impact-absorbing layer 120 can line the inner surfaces of a hard-shell case to form a protective case having an impact-absorbing layer. In another example, the impact-absorbing layer 120 can line shipping containers to protect fragile or sensitive cargo during transit.

In one example, a protective helmet 100 can include a hard outer shell 105 having an exterior surface and an interior surface. The protective helmet 100 can include an impact-absorbing layer 120 adjacent to and conforming to the interior surface of the hard outer shell 105. The impact-absorbing layer 120 can include a base layer 140 and a plurality of flexible raised portions 135 extending from the base layer. The plurality of flexible raised portions 135 can each have a base portion wider than an end portion, as shown in FIG. 4. The end portions of the flexible raised portions 135 can extend to and contact the interior surface of the hard outer shell 105, as shown in FIG. 2. The end portions of the plurality of flexible raised portions 135 can be affixed to or captured in pockets or indentions on the interior surface of the hard outer shell 105. The plurality of flexible raised portions 135 can be made of microcellular urethane foam having a density of about 1-30 pounds per cubic foot. The microcellular urethane foam can be a mechanically frothed microcellular urethane foam. The microcellular urethane foam can have a density of about 10-20, 10-18, or 12-18 pounds per cubic foot. The plurality of flexible raised portions 135 can each be defined by a side angle, a top radius, and a base radius, as shown in FIG. 4. The side angle can be about 1-30, 10-20, or 15 degrees. The base radius can be about 0.005-1.5, 0.125-0.5, or 0.125-0.25 inches. The top radius is about 0.005-1.0, 0.125-0.5, or 0.125-0.25 inches.

The protective helmet 100 can include an adjustable suspension system 101 having a fabric layer 125 configured to conform to a portion of a wearer's head and a plurality of tethers 130 extending from the fabric layer 125 to the hard outer shell 105 to flexibly secure the fabric layer 125 to the hard outer shell 105 and to capture the impact-absorbing layer 120 between the fabric layer 125 and the hard outer shell 105. The tethers 130 can be configured to allow the hard outer shell 105 to rotate relative to the fabric layer 125 during an impact event as one or more of the plurality of flexible raised portions 135 topple over, as shown in FIG. 3.

As shown in FIG. 37, an adjustable suspension system 101 can include a first fabric layer 125 configured to conform to a front portion of a wearer's head 150 and a second fabric layer 126 configured to conform to a rear portion of the wearer's head 150. The first fabric layer 125 can attach to the second fabric layer 126 at a first attachment point along a left side of the wearer's head and at a second attachment point 160 along a right side of the wearer's head. The adjustable suspension system 101 can include a tensioning strap 145 extending from the first attachment point to the second attachment point 160 and having a chin cup 116 configured to be secured against a wearer's chin. The adjustable suspension system 101 can include a plurality of tethers 130 extending from the first and second fabric layers (125, 126) to the hard outer shell 105 to flexibly secure the first and second fabric layers to the hard outer shell and to capture the impact-absorbing layer 120 between at least one of the first and second fabric layers (125, 126) and the hard outer shell 105. The plurality of tethers 130 can be configured to allow the hard outer shell 105 to rotate relative to the first and second fabric layers (125, 126) during an impact event as one or more of the plurality of raised portions 135 topple over, as shown in FIG. 3.

As shown in FIG. 3, the tethers 130 can limit rotation of the hard outer shell 105 to prevent over-rotation of the hard outer shell during an impact. In some examples, the tethers 130 can be sacrificial and can be configured to break when exposed to a predetermined tension, thereby permitting the tethers 130 to dissipate a portion of the impact force. In this example, the tethers 130 can be replaceable and selectable based on a predetermined tension at which the tether is designed to break.

The base layer 140 of the impact-absorbing layer 120 can include an indentation 175 on a bottom surface of the base layer beneath one of the plurality of flexible raised portions 135. The indentation 175 can be configured to provide a cavity 176 in the impact-absorbing layer 120 to increase an initial compression rate of the flexible raised portion during an impact event. The impact-absorbing layer can include a vent 180 extending from a top surface of the impact-absorbing layer 120 to the indentation 175 on the bottom surface of the impact-absorbing layer. Compressing the flexible raised portion 135 during an impact event can collapse the flexible raised portion downward into the cavity 176 formed by the indentation 175 thereby forcing air out of the cavity 176 through the vent. The air that is forced out of the cavity 176 is capable of transporting heat and perspiration away from the player's head 150, thereby cooling the player's head and helping to prevent heat exhaustion.

In another example, a protective helmet 100 can include a hard outer shell 105 having an exterior surface and an interior surface. The protective helmet 100 can include an adjustable suspension system 101 having a fabric layer 125 configured to fit snugly over a portion of a wearer's head 150. The fabric layer 125 can be flexibly connected to the interior surface of the hard outer shell 105 by two or more tethers 130. The fabric layer 125 can be connected to a chin cup 116 by a tensioning strap 145. Tightening the tensioning strap 145 can simultaneously draw the chin cup 116 against a wearer's chin and draw the fabric layer 125 against the portion of the wearer's head 150. The protective helmet 100 can include an impact-absorbing layer 120 captured between the fabric layer 125 and the hard outer shell 105. The impact-absorbing layer 120 can include a plurality of flexible raised portions 135 extending outward from a base layer 140 toward the interior surface of the hard outer shell 105. End portions of the plurality of raised portions 135 can be affixed to or captured by pockets or depressions on the interior surface of the hard outer shell 105. The hard outer shell 105 can be configured to rotate relative to the fabric layer 125 during an impact event as the flexible raised portions 135 of the impact-absorbing layer topple over, as shown in FIG. 3.

The impact-absorbing layer 120 can be made of a microcellular urethane foam. The microcellular urethane foam can have a density of about 10-20, 10-18, or 12-18 pounds per cubic foot. The plurality of flexible raised portions 135 can each have a side angle (θ), a top radius R₂, and a base radius R₁. The side angle (θ) can be about 1-30, 10-20, or 15 degrees. The base radius R₁ can be about 0.005-1.5, 0.125-0.5, or 0.125-0.25 inches. The top radius R₂ can be about 0.005-1.0, 0.125-0.5, or 0.125-0.25 inches.

The base layer 140 can include an indentation 175 on a bottom surface of the base layer 140 beneath one of the plurality of raised portions 135. The indentation 175 can be configured to provide a cavity 176 in the impact-absorbing layer 120 to increase an initial compression rate of the flexible raised portion 135 during an impact event. The impact-absorbing layer 120 can include a vent 180 extending from a top surface of the impact-absorbing layer to the indentation 175 on the bottom surface of the impact-absorbing layer. Compressing the flexible raised portion 135 during an impact event can collapse the raised portion 135 downward into the cavity 176 formed by the indentation 175 thereby forcing air out of the cavity 176 through the vent 180. The air forced out of the cavity 176 is capable of transporting heat and perspiration away from the player's head 150, thereby cooling the player.

In yet another example, an impact-absorbing layer 120 can include a base layer 140 and one or more flexible raised portions 135 extending from the base layer. Each of the one or more flexible raised portions 135 can have a base portion wider than an end portion. The one or more flexible raised portions 135 can each be defined by a side angle (θ), a top radius R₂, and a base radius R₁, where the side angle is about 10-20 degrees, the base radius R₁ is about 0.05-1.0 inches, and the top radius R₂ is about 0.05-1.0 inches. The base layer 140 can have a thickness (t) of about 0.1-1.3 inches.

The impact-absorbing layer 120 can be made of a microcellular urethane foam having a density of about 12-18 pounds per cubic foot. The microcellular urethane foam can be a mechanically frothed urethane foam formed by a manufacturing process that includes casting a liquid froth onto a substrate, heat curing the liquid froth to form a solid urethane foam, and coating the solid urethane foam with a continuous skin made of a thermoplastic elastomer. The substrate can be a mold having a shape that produces a solid urethane foam having a shape corresponding to the impact-absorbing layer 120 with flexible raised portions 135 extending from a base layer 140.

The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the claims to the embodiments disclosed. Other modifications and variations may be possible in view of the above teachings. The embodiments were chosen and described to explain the principles of the invention and its practical application to enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art. As used herein, the term “about” means plus or minus five percent. 

What is claimed is:
 1. A protective helmet comprising: a hard outer shell comprising an exterior surface and an interior surface; and an impact-absorbing layer adjacent to and conforming to the interior surface of the hard outer shell, the impact-absorbing layer comprising a base layer and a plurality of flexible raised portions extending from the base layer, wherein the plurality of flexible raised portions each has a base portion wider than an end portion, wherein the end portions of the flexible raised portions extend to and contact the interior surface of the hard outer shell, and wherein the plurality of flexible raised portions comprise a microcellular urethane foam having a density of about 1-30 pounds per cubic foot.
 2. The protective helmet of claim 1, wherein the microcellular urethane foam is a mechanically frothed microcellular urethane foam.
 3. The protective helmet of claim 1, wherein the microcellular urethane foam has a density of about 10-20, 10-18, or 12-18 pounds per cubic foot.
 4. The protective helmet of claim 1, wherein the plurality of flexible raised portions are each defined by a side angle, a top radius, and a base radius, and wherein the side angle is about 1-30, 10-20, or 15 degrees.
 5. The protective helmet of claim 4, wherein the base radius is about 0.005-1.5, 0.125-0.5, or 0.125-0.25 inches, and wherein the top radius is about 0.005-1.0, 0.125-0.5, or 0.125-0.25 inches.
 6. The protective helmet of claim 1, further comprising an adjustable suspension system comprising: an inner fabric layer configured to conform to a portion of a wearer's head; and a plurality of tethers extending from the inner fabric layer to the outer shell to flexibly secure the fabric layer to the hard outer shell and to capture the impact-absorbing layer between the fabric layer and the hard outer shell, wherein the tethers are configured to allow the hard outer shell to rotate relative to the inner fabric layer during an impact event as one or more of the plurality of flexible raised portions topple over.
 7. The protective helmet of claim 1, further comprising an adjustable suspension system comprising: a first fabric layer configured to conform to a front portion of a wearer's head; a second fabric layer configured to conform to a rear portion of the wearer's head, wherein the first fabric layer attaches to the second fabric layer at a first attachment point along a left side of the wearer's head and at a second attachment point along a right side of the wearer's head; a tensioning strap extending from the first attachment point to the second attachment point and comprising a chin cup configured to be secured against a wearer's chin; a plurality of tethers extending from the first and second fabric layers to the hard outer shell to flexibly secure the first and second fabric layers to the hard outer shell and to capture the impact-absorbing layer between at least one of the first and second fabric layers and the hard outer shell, wherein the plurality of tethers are configured to allow the hard outer shell to rotate relative to the first and second fabric layers during an impact event as one or more of the plurality of flexible raised portions topple over.
 8. The protective helmet of claim 1, wherein the base layer comprises an indentation on a bottom surface of the base layer beneath one of the plurality of flexible raised portions, wherein the indentation is configured to provide a cavity in the impact-absorbing layer to increase an initial compression rate of the flexible raised portion during an impact event.
 9. The protective helmet of claim 8, further comprising a vent extending through the impact-absorbing layer from a top surface of the impact-absorbing layer to the indentation on the bottom surface of the impact-absorbing layer, wherein compressing the flexible raised portion during an impact event collapses the raised portion downward into the cavity formed by the indentation thereby forcing air out of the cavity through the vent, the air capable of transporting heat and perspiration away from the player's head.
 10. The protective helmet of claim 1, wherein the end portions of the plurality of flexible are affixed to or captured by the interior surface of the hard outer shell.
 11. A protective helmet comprising: a hard outer shell comprising an exterior surface and an interior surface; an adjustable suspension system comprising: a fabric layer configured to fit snugly over a portion of a wearer's head, the fabric layer being flexibly connected to the interior surface of the hard outer shell by two or more tethers, the fabric layer being connected to a chin cup by a tensioning strap, wherein tightening the tensioning strap simultaneously draws the chin cup against a wearer's chin and draws the fabric layer against the portion of the wearer's head; an impact-absorbing layer captured between the fabric layer and the hard outer shell, wherein the impact-absorbing layer comprises a plurality of flexible raised portions extending outward from a base layer toward the interior surface of the hard outer shell, wherein the hard outer shell is configured to rotate relative to the fabric layer during an impact event as the flexible raised portions of the impact-absorbing layer topple over.
 12. The protective helmet of claim 11, wherein the impact-absorbing layer comprises a microcellular urethane foam.
 13. The protective helmet of claim 12, wherein the microcellular urethane foam has a density of about 10-20, 10-18, or 12-18 pounds per cubic foot.
 14. The protective helmet of claim 11, wherein the plurality of flexible raised portions each comprise a side angle, a top radius, and a base radius, and wherein the side angle is about 1-30, 10-20, or 15 degrees.
 15. The protective helmet of claim 14, wherein the base radius is about 0.005-1.5, 0.125-0.5, or 0.125-0.25 inches, and wherein the top radius is about 0.005-1.0, 0.125-0.5, or 0.125-0.25 inches.
 16. The protective helmet of claim 11, wherein the base layer comprises an indentation on a bottom surface of the base layer beneath one of the plurality of flexible raised portions, wherein the indentation is configured to provide a low density cavity in the impact-absorbing layer to increase an initial compression rate of the raised portion during an impact event.
 17. The protective helmet of claim 11, further comprising a vent extending through the impact-absorbing layer from a top surface of the impact-absorbing layer to the indentation on the bottom surface of the impact-absorbing layer, wherein compressing the raised portion during an impact event collapses the raised portion downward into a cavity formed by the indentation thereby forcing air out of the cavity through the vent, the air capable of transporting heat and perspiration away from the player's head.
 18. The protective helmet of claim 11, wherein end portions of the plurality of flexible raised portions are affixed to or captured by the interior surface of the hard outer shell.
 19. An impact-absorbing layer comprising: a base layer; and one or more flexible raised portions extending from the base layer, each of the one or more flexible raised portions having a base portion wider than an end portion, the one or more flexible raised portions each being defined by a side angle, a top radius, and a base radius, wherein the side angle is about 10-20 degrees, wherein the base radius is about 0.05-1.0 inches, wherein the top radius is about 0.05-1.0 inches, wherein the base layer has a thickness of about 0.1-1.3 inches, and wherein the impact-absorbing layer comprises a microcellular urethane foam having a density of about 12-18 pounds per cubic foot.
 20. The impact-absorbing layer of claim 19, wherein the microcellular urethane foam is a mechanically frothed urethane foam formed by a manufacturing process comprising: casting a liquid froth onto a substrate; heat curing the liquid froth to form a solid urethane foam; and coating the solid urethane foam with a continuous skin comprising a thermoplastic elastomer. 